Method of manufacturing transformer cores



Nov. 18, 1958 e. A. SMITH 2,850,405

METHOD OF MANUFACTURING TRANSFORMER CORES Filed May 14, 1956 2Sheets-Sheet 1 H FIG.|. A 23V FIG.2.

INVENTOR GEORGE A. SMITH m. is, 1958 a. A. SMITH 2,850,405

METHOD OF MANUFACTURING TRANSFORMER CORES I Filed May 14, 1956 2Sheets-Sheet 2 FIG. 6.

V E i FIG] INVENTOR GEORGE A SMITH the core.

METHOD OF MANUFACTURING TRANSFORMER CORES George A. Smith, Pine Bluff,Ark., assignor to Central Transformer Corporation, Pine Bluff, Ark., acorporation of Arkansas Original application July 5, 1955, Serial No.519,965. Divided and this application May 14, 1956, Serial No. 584,575

5 Claims. (Cl. 29-15557) This invention relates to a method formanufacturing transformer cores.

This application is a division of my copending application Serial No.519,965, filed July 5, 1955.

In particular this invention relates to the method used and productobtained in the manufacture of so-called wound-type magnetic cores usingmagnetic rolled metal strip of suitable composition, wherein thelamination layers of the cores are annealed, cut, and then subsequentlylinked with a pre-formed electrical winding or windings of atransformer.

Heretofore in the manufacture of such cores after the core has beenlinked with said windings the ends of the lamination layers of the coreshave been joined in various ways. In one method of manufacturetheindividual lamination layers have been joined by butting the ends ofsaid layers to form a so-called butt joint, wherein the joints are inalinement. This method of joining results in high core losses since thejoints cause a gap in the magnetic circuit. Another method of joininghas been to overlap the ends of the layers to form a so-called lap jointcore. This method results in a build-up in the cross sectional area ofthe core at the joints since the overlapping ofv the layers produces asection which has substantially twice as many lamination layers as theother sections of In addition to providing a core which is undesirablybulky in the area of the lap joints, in this type of core more materialis required than for the butt joint type since extra material must beprovided to form the overlapping portions.

' Therefore, this invention is directed to a novel method and productthereof which overcomes the above mentioned disadvantages and objectionsin magnetic cores and their manufacture. These disadvantages areovercome by providing in the present invention a novel method forjoining the lamination layers of the magnetic cores of transformers,which produces a productuniforrn in cross sectional area throughout,which is economical to manufacture and which has excellent magneticproperties.

The principal object of the present invention is to provide a new andimproved method of manufacturing transformer cores.

I A further object of the invention is to provide a method 'ofmanufacturing cores for transformers which includes the steps of forminga trapezoidal coil of magnetic strip material having a major short sideand a shorter minor short side, forming a trapezoidal coil of magneticstrip material having a major short side, substantially equal in lengthto the first mentioned minor short side and a shorter minor shortside,annealing said trapezoidal coils, subsequently severing the firstmentioned coil across its major short side and the last mentioned coilacross its minor short side, and thereafter overlapping ends oflamination layers from the first mentioned coil as severed andinterleaving lamination layers from the last mentioned coil as severedbetween the successive lapped layers.

. A further object of the invention is to generally im- United StatesPatent prove the construction and method of manufacture of transformercores. 7 v

The means by which the foregoing and other objects of the presentinvention are accomplished and the manner of their accomplishment willbe readily understood from the following specification upon reference tothe accompanying drawings, in which: v

Fig. 1 is an elevational view of one of a pair of mandrels used in themanufacture of the magnetic cores showing the magnetic metalstripb'ein'g wound thereon.

Fig. 2 is an elevational view of the other of a pair of mandrelssimilarly showing magnetic metal strip being wound thereon.

Fig. 3 is an elevational view of the core winding wound on the mandrelof Fig. 1, in the process of manufacture.

Fig.4 is an elevational view of the core winding wound on the mandrel ofFig. 2, in the process of manufacture.

Fig. 5 is an elevational view of the core winding of Fig. 3 after thelamination layers have been severed.

Fig. 6 is an elevational view of the core winding of Fig. 4 after thelamination layers have been severed and the stacked layers have beenshaped.

Fig. 7 is an elevational view of a transformer coil with one core linkedtherewith and the other core in the course of linking, certain partsbeing broken away for purposes of illustration.

Referring now to the drawings in which the various parts are indicatedby numerals, the construction of the transformer core of the presentinvention is begun by winding a magnetic metal strip 11, having asuitable width and thickness, onto a preferably trapezoidal-shapedmandrel 13. The magnetic strip is preferably ofv the type which has amost favorable magnetic direction which is along the length of strip,such as cold rolled steel strip. Mandrel 13 is adapted to be mounted ona shaft 14 of a winding lathe (not shown). Fig. 1 illustrates thewinding process with the mandrel illustrated as being ro tated in aclockwise direction, although it is obvious that the winding may beperformed with the mandrel being rotated in either direction. The longerside 15 of the two unequal sides of mandrel 13 is of a length which isequal to the length of the shorter side 17 of said unequal sides plusany given length. For clarity, said given length will be denoted X andthe length of shorter side 17 will be denoted Y. Thus longer side 15 isequal to X plus Y.

The winding of magnetic strip 11 onto mandrel 13 is continued until thedesired number of turns have been wound on said mandrel. The strip 11 isthen severed from the supply reel leaving the winding A, comprising aplurality of lamination layers, formed around mandrel 13. The termlamination layers is used herein to refer to the individual layers sinceone or more laminations of magnetic strip material may be included ineach of the said layers. Winding A is removed from the mandrel andbanded with suitable banding straps 19, as preferably of steel, whichare preferably wrapped around the equal length legs of the winding A tohold the turns firmly in place. Additionally a strap 21, as preferablyof steel, is fastened so as to encircle the two legs of equal length ofwinding A to hold said legs inwardly, thereby substantially maintainingthe shape of the winding as formed shown). Fig. 2 illustrates thewinding process with the mandrel illustrated as being rotated in aclockwise direction, although it is obvious that the winding may beperformed with the mandrel being rotated in either direction. The twoequal length sides 27 of mandrel 25 are substantially the same length asthe two equal length sides 29 of mandrel 13, and the longer side 31 ofthe two unequal sides of mandrel 25 is substantially equal to theshorter side 17 of the two unequal sides of mandrel.13. Thus, since asheretofore described, side 17 is equal to length Y and since side 31 isequal to side 17, it follows that side 31 is equal to length Y. Theshorter side 32 of the unequal sides of mandrel 25 is of a length whichis equal to longer side 31 minus said given length X. Thus side 32 isequal to Y minus X.

The winding of magnetic strip 23 onto mandrel 25 is continued until thedesired number of turns have been wound on said mandrel. The strip 23 isthen severed from the, supply reel leaving the winding B, comprising aplurality of lamination layers, formed around mandrel 2 It will beapparent that it is preferable to wind substantially the same number ofturns on mandrel as, manfilfll, .3 since the lamination layers fromthese two,- mandrelswill subsequently be combined, as will be and in amanner similar to winding A is handed with banding straps 19 and strap21, thereby substantially maintaining the shape of the winding as formedon the mandrel.

It will be understood that the trapezoidal windings A and B have thesame relative dimensions as mandrels 13 and 25, respectively. Thus theequal legs 33 of winding A are. the same length as the equal legs 34 ofwinding B. The shorter leg 35 of the, unequal legs of winding A is thesame length as the longer leg 36 of the unequal legs of winding B. Thelonger leg 37 of the unequal legs of winding A exceeds the shorter leg35 by the same amount that the longer leg 36 of winding B exceeds theshorter leg 38. In other words, the length of leg 37 equals the lengthof leg 35 plus X and the length of leg 36 equals the length of leg 38plus X.

Windings A and B, as bound, are then annealed in an oven having an inertatmosphere to relieve the stresses in the strip which were formed duringthe winding operation, thereby improving the magnetic properties of thestrip. Additionally the annealing sets the shape of the windingssubstantially as bound.

Theturns of windings A and B are then respectively cut through on aplane perpendicular to and substantially at the mid-section of thelonger leg 37 of the two unequal legs of winding A and on a planesubstantially at the I midsection of the shorter'leg 38 of the twounequal legs of winding B, thereby dividing the legs 37, 38 intosubstantially equal length and portions 37A, 37B and 38A, 38B,respectively, and forming individual discontinuous lamination layers.sections of the legs 37, 38 of the windings A and B are indicated at 39,40, respectively. The cutting may be performed by any suitable means, asfor example by sawing or by severing the turns with a cutting wheel orthe like. The lamination layers of winding B are then spread tosubstantially rectangular shape with legs 34 of the windingsubstantially at right angles to uninterrupted leg 36 and with thedivided end portions 38A, 38B projecting substantially at right anglesfrom the opposite ends of the respective legs. Subsequent to the cuttingoperation and spreading operation of winding B, the straps 19, 21 areremoved from winding A and B. Fig. 5 and Fig. 6 show the stacks oflayers formed from windings A and B, respectively, after this step inthe process of manufacture.

For convenience the lamination layers of the respective windings arenumbered consecutively, beginning with the inner layers, and have as asufiix the letter A or B to designate the windings A or B. Thus,referring to Fig. 5., the inner lamination layer of winding A isdesignated The cuts through these mid- 41A and the successive outwardlamination layers designated 42A, 43A and 44A. Referring to Fig. 6, theinner lamination layer of winding B is designated 41B and the successiveoutward lamination layers designated 42B, 43B and 44B. It will beunderstood that only four layers of each winding havebeen shown forpurposes of illustration and that any number of layers may be includedin the windings, depending upon the desired crosssectional area of thefinished core.

The lamination layers of windings A and B are then assembled with atransformer coil 45 in the following manner. The first step in thisassembly operation is to separate layer 41B from winding B and to linkthis layer with coil 45. This linking is accomplished by spreading thesevered ends of layer 413 and inserting one of said ends through thehollow central or window portion 46 of coil 45 and the other of saidends around the outside of the coil in a manner similar to thatillustrated in Fig. 7' which shows layer 44B being so linked. It shouldbe noted that in separating the ends of the turns during the process oflinking with coil 45, the amount of separation is small enough so thatthe elastic limit of the annealed turns is not reached, thereby notimpairing the magnetic properties of the strip material. For conveniencethe ends of the layers which are inserted through the central portion 46will hereinafter be designated inner ends and the ends which encirclethe outer periphery of the coil will be designated outer ends.

The inner layer 41A of winding A is then linked in a similar manner tothe opposite side of coil 45 and the ends of the layer 41A areoverlapped by said given length X, as shown in Fig. 7, the inner end ofthe layer being lapped on top of the outer end of the layer. The nextlayer 42A of winding A is then linked on coil 45 over layer 41B, theinner end of the layer 42B being brought into abutment with the outerend of layer 41B and the outer end of layer 42A being lapped on top ofthe inner end of layer 42A by said given length X. The next layer 42B ofwinding B is then linked on coil 45 over layer 41A, the outer end oflayer 42B being brought into abutment with the inner end of layer 41A.It will be noted that in the assembly of the layers the amount ofoverlap of the lapped layers may be varied some to insure firm abutmentwith the previously stacked underlying layer. This process of assemblyis continued by consecutively stacking the even numbered layers fromwinding A alternately with the consecutive odd numbered layers fromwinding B to form core 47. Core 49 is similarly formed by consecutivelystacking the odd numbered layers from winding A alternately with theconsecutive even numbered layers from winding B.

Thus it will be understood a pair of cores 47, 49 of concentricallystacked lamination layers are formed which include an improved jointmeans, having in every other layer a lap joint alternated withbutt-joint layers and having the butt joints in staggered relationship.It is obvious that the lap joints will have a length of overlapsubstantially equal to the heretofore designated amount X and the endsof the turns from winding B will be spaced by substantially this sameamount X. Thus it is obvious that the length of the sides of themandrels 13, 25 may be chosen to give the desired length of overlap inthe finished cores.

It will be understood that from this method of manufacture magneticcores are formed which are uniform in cross sectional area, therebyusing the strip material to the best advantage and eliminating anyundesirable bulky build-up sections in the core. By this arrangement agreat savings is realized in the manufacturing cost as compared withprevious lap joint cores since in previous cores excess material isneeded to form the lap, and yet in this arrangement the advantages ofthe lap joint in individual continuous lamination layers are maintained.

Although the formation of a pair of coresfor one type of transformer hasbeen described, it should be understood that the inventionis not limitedto a pair of cores for this particular type, but other transformer typesmay be formed. For example, windings A and B may be combined to form asingle core linked with a pair of transformer coils.

Also it will be understood that other details of the method andconstruction illustrated and described may be altered without departingfrom the spirit of the invention as defined by the following claims.

I claim:

1. In the method of constructing a transformer comprising the steps ofwinding magnetic strip material on a first trapezoidal mandrel andwinding magnetic strip material on a second trapezoidal mandrel to forma first trapezoidal winding and a second trapezoidal winding, eachcomprising a plurality oflamination layers, the equal legs of said firsttrapezoidal winding being formed to have the same length as the equallegs of said second winding, the shorter of the parallel legs of saidfirst winding being equal to the longer of the parallel legs of saidsecond winding, the longer of the parallel legs of each of said windingsrespectively exceeding the shorter of the legs of each of said windingsby the same amount, removing said windings from said mandrels andbinding said windings with straps to hold the windings in substantiallytheir wound trapezoidal shape, annealing said winding in said shape toremove the strains and to set the windings in said shape, cuttingthrough the longer parallel leg of said first winding in a planesubstantially at the mid point between the equal legs and cuttingthrough the shorter parallel leg of said second winding in a planesubstantially at the mid point between the equal legs, removing saidstraps from the windings, removing alternate lamination layers from thewindings in sequence beginning at the inside lamination layers of thewindings, building a core linked with one side of the coil of saidtransformer by concentrically stacking in said sequence the alternatelamination layers removed from the first winding with the alternatelamination layers removed from the second winding, building a secondcore linked with the other side of the coil of said transformer bystacking in said sequence the remaining lamination layers removed fromthe first winding alternately with the remaining lamination layersremoved from the second winding, concurrently with the stacking of thetwo cores overlapping the ends of the lamination layers from said firstwinding and abutting the ends of the lamination layers from said secondwinding with the ends of the lamination layers of said first winding.

2. In the method of constructing a transformer comprising the steps ofwinding magnetic strip material on a first trapezoidal mandrel andwinding magnetic strip material on a second trapezoidal mandrel to forma first trapezoidal winding and a second trapezoidal winding, eachwinding comprising a plurality of lamination layers, the equal legs ofsaid first-trapezoidal winding being formed to have the same length asthe equal legs of said second winding, the shorter of the parallel legsof said first winding being equal in length to the longer of theparallel legs of said second winding, the longer of the parallel legs ofeach of said windings respectively exceeding the shorter of the legs ofeach of said windings by the same amount, removing said windings fromsaid mandrels and binding said windings with straps to hold the windingsin substantially their wound trapezoidal shape, annealing said windingsin said shape to remove the strains and to setv the windings in saidshape, cutting through the longer parallel leg of said first winding ina plane substantially at the mid point between the equal legs andcutting through the shorter parallel leg of said second winding in aplane substantially at the mid point between the equal legs, removingsaid straps from the windings, removing alternate lamination layers fromthe windings in sequence beginning at the inside lamination'layers ofthelwindings, building a core'liiike'd" with the coil of saidtransformer by concentrically stack ing in said sequence the alternatelamination layers removed from the first winding alternately with thealternate lamination layers removed from the second winding,concurrently with the stacking of said core overlapping the ends of thealternate lamination layers from said firstwinding and abutting the endsof the alternate lamination layers from said second winding with theends of the alternate lamination layers from said first winding.

3. In a method of constructing a transformer comprising the steps ofwinding magnetic strip material on a first trapezoidal mandrel andwinding magnetic strip material on a second trapezoidal mandrel to forma first trapezoidal winding and a second trapezoidal winding, eachwinding comprising a plurality of lamination layers, the equal legs ofsaid first trapezoidal winding being formed to have the same length asthe equal legs of said second winding, the shorter of the parallel legsof said first windin'g being equal to-the longer of the parallel legs ofsaid:

second winding, the longer of the parallel legs of each' of saidwindings respectively exceeding the shorter of the legs of each of saidwindings by the same amount, holding said first winding and said secondwinding in substantially their wound trapezoidal shape and annealingsaid windings while being so held to remove the strains and to set thewindings in said shape, cutting through the longer parallel side of saidfirst winding in a plane substantially at the mid point between theequal sides and cutting through the shorter parallel side of said secondwinding in a plane substantially at the mid point between the equalsides, removing the lamination layers from the windings in sequencebeginning at the inside layer of the windings, building a core linkedwith one side of the coil of said transformer by concentrically stackingin said sequence the alternate lamination layers removed from the firstwinding alternately with the alternate lamination layers removed fromthe second winding, building a second core linked with the other side ofthe coil of said transformer by stacking in said sequence the remaininglamination layers removed from the first winding alternately with theremaining lamination layers removed from the second winding,concurrently with the stacking of the two cores overlapping the ends ofthe lamination layers from said first winding and abutting the ends ofthe lamination layers of said second winding with the ends of thelamination layers of said first winding.

4. In the method of constructing a transformer comprising the steps ofwinding magnetic strip material on a first trapezoidal mandrel andwinding magnetic strip material on a second trapezoidal mandrel to forma first trapezoidal winding and a second trapezoidal winding, eachwinding comprising a plurality of lamination layers, the equal legs ofsaid first trapezoidal winding being formed to have the same length asthe equal legs of'said second winding, the shorter of the parallel legsof said first winding being equal to the longer of the parallel legs ofsaid second winding, the longer of the parallel legs of each of saidwindings respectively exceeding the shorter of the legs of each of saidwindings by the same amount, holding said first winding and said secondwind-- ing in substantially their wound trapezoidal shape and annealingsaid windings while being so held to remove the strains and to set thewindings in said shape, cutting through the longer parallel side of saidfirst winding in a plane substantially at the midpoint of the equalsides and cutting through the shorter parallel side of said secondwinding in a plane substantially at the midpoint of the equal sides,removing the lamination layers from the windings in sequence beginningat the inside lamination layers of the windings, building a core linkedwith one side of the coil of said transformer by concentrically stacking in said sequence the alternate lamination layers removed from thefirst winding alternately with the alter uilding; ;s c .p d or l nked-1i hlt e oth rL side of. the; oiln fi said ansformer yr ta lsingsiniaidsequ nqe the;

rem ininst amina. an. l y rst moy from the first wind:v ing alternatelywith-the remaining laminatipn layers removed from the second winding,concurrentlvwith the a ing? the; w i ares. ov l pping e; nds. =c fv e.

lamination. 5 layers- ;from said first; winding and abutting h nds e minion l y rs f om-s i ec nd twindw n k th h nds f t the l n tion layers 1of i s id :first ind n 5. In the method of construeting a transformercore comprising the, steps of winding, magnetic strip material on a first trapezoidal mandrel and windinglmagnetic strip material on asecondtrapezoidal nnan'ldrel; tor form a first trapezoidal windingand asecond;trapezoidal ;winding,

each winding comprisinga pluralityio fi laminatiomlayers, he qu l s. ofi 1 fi st rapezoid l dingr being formed to have the same length asthe-equal legs of said second winding, the shorter- I of ;-the:parallel-legs ,oftfsaid first winding-beingequal topthealonger; of,themaralld legs of said second winding, theJonger ofi g-thelparal-lellegs ofi; each 10f, isaidiwindings -:respectively. exceeding the shorterof thew-legs oil-each r0.'said windings by.the same am91 nt,;,ho1ding;said;first;r winding:.and said second windsaid ;se eond;windingto.;form, a;c0re having alternate lap an'd staggered';buttuioints,said.lap joints being formed in the respective individual lamination 7 layersof the said first winding and;,said ,c0re being formed with asubstanllyn iqr firossisec onalar a:

No. references cited.

